1. Field of the Invention
This invention relates to apparatus for closing filled sacks, which have been transferred by a conveyor from a filling station to a closing station, comprising a gripper, which, like pliers, grips the opening-defining edges of the filled sacks and presents them to a pair of gripping rollers, rotatable about axes at right angles to the main long axis of the sack. The apparatus also comprises closing means, which are located adjacent the gripper and serve to form a seam for closing the opening-defining edge portions of the sack which are being held in flat surface contact with each other.
2. Description of the Prior Art
In related apparatus which is known from Austrian Patent Specification No. 363,851, the closing means consist of pivoted welding jaws, which cooperate like pliers and form a top seam weld for closing the opening-defining edges, the marginal portions of which are in flat surface contact with each other. The two welding jaws are carried by respective arms and a U-shaped member is pivoted to each of said arms and carries a pressure-applying roller. As the welding jaws approach their welding position the pressure-applying roller is pivotally moved against the action of a spring from a position in which the roller is remote from the welding jaw to a position in which the roller is adjacent to the welding jaw so that the roller moving between said two positions squeezes air out of the sack and moves the gaping edge portions which define the opening into a closed position with the edge portions in contact with each other and holds them closed in that position until they are contacted by the welding jaws.
German Patent Specification No. 26 29 065 and the corresponding U.S. Pat. No. 4,115,978 granted on an application filed June 24, 1977, disclose an apparatus for closing filled sacks. That apparatus comprises a drum-like feeder, which rotates about a horizontal axis and is provided with four pairs of plier-like grippers, which are distributed around the periphery of the drum. When the sacks have been filled and the opening-defining edge portions have been pulled together to a flat shape, the feeder deposits the filled sacks on a belt conveyor in such a manner that, in the deposited sacks, the closed lips which are formed by the opening-defining edge portions, protrude beyond the grippers and assume a horizontal position so that said closed lips can be provided between the jaws of a welding apparatus that makes a transverse seam weld closing the sacks. That known apparatus can be used to close the flattened transverse opening-defining edge portions of plastic sacks or plastic-coated sacks by means of transverse seam welds if the lips or borders formed by the superimposed edge portions which define the opening of the sack protrude beyond the grippers to a sufficiently large extent. But difficulties arise if the lips are too short or of insufficient width or if the sacks are to be closed by stitched seams which requires longer or wider lips, borders or margins.